1. The way of force
Bolts are generally subjected to various external forces during use, such as tensile, bending, compression and other external forces. These external forces may exist at the same time. When multiple external forces are applied to the bolt at the same time, especially in the case of overload, Bolts are likely to break.
In order to prevent this phenomenon, we should choose appropriate materials and specifications when selecting bolts to increase the compressive strength and tensile capacity of the bolts.
2. Corrosion
Corrosion is a common cause of cracking in fasteners. Corrosion includes physical corrosion, chemical corrosion, and pitting corrosion. Here we focus on pitting corrosion. Most people are not very clear about the principle of this kind of corrosion. These materials form a link pair. When tightening with the workpiece, due to the different point solutions of various materials, electron flow will be generated to form micro batteries. In the case of humidity, the point solution corrosion is more serious.
To prevent this phenomenon, we need to maintain a dry environment to prevent this reaction from happening.
3. Hydrogen embrittlement
The occurrence of hydrogen embrittlement is a fatal defect for high-strength bolts. Once it encounters external force, it is easy to crack. There are two main reasons for the occurrence of hydrogen embrittlement, one is internal, which occurs by material smelting, which rarely occurs. The second type is external. After the hydrogen atoms in the free state during pickling and electroplating occur, they will be embedded in the matrix and dispersed into the interior, damaging the original equilibrium state, causing lattice distortion and cracking under the effect of external force.
An effective treatment to prevent this phenomenon is to use dehydrogenation annealing.
4. Planning and craftsmanship
The tooth root garden is neglected in the design or the cusps are sharp when rolling; wrinkles and pits occur when the screw is hot-rolled. The occurrence of these sharp corners and grooves is the main factor for the occurrence of cracks.
In order to prevent this phenomenon, we should pay attention to this problem in planning and manufacturing to avoid the occurrence of potential cracks. Fasteners encounter the second type of temper brittleness in the process of quenching and tempering, and the occurrence of such temper brittleness should be minimized.
5. Device and connection
If the torque is too small, the pre-tightening force is too small, and the locking force may be loosened under the condition of oscillation or operation. However, if the torque is too large or even exceeds the specified value, the thread will work under overload conditions. When various external forces are applied in combination , it is likely to cause wire drawing and tripping to cause failure.
In order to prevent this phenomenon, the installation torque should be within the specified range, and the installation should be carried out according to the specified torque. In particular, it is necessary to understand the torque coefficients of various materials and various surface treatments, and use the correct torque value to prevent the failure of the connection pair.
